Multilayer film containing amorphous nylon

ABSTRACT

An oriented multilayer film comprising a barrier layer, a first layer on one side of said barrier layer and a second layer on the opposite side of said barrier layer is provided for use in food packaging applications. The first and second layers have melting points of at least about 115° C. The barrier layer comprises amorphous nylon having a glass transition temperature greater than the higher of the two melting points or higher than the melting point of the first and second layers. The barrier layer is substantially impermeable to oxygen, while the first and second layers may comprise certain polyethylene resins. The oxygen barrier properties of the film do not deteriorate as the barrier layer gradually absorbs moisture. A process for making such multilayer films is also provided.

FIELD OF THE INVENTION

This invention relates to oriented multilayer films for use in barrierpackaging applications.

BACKGROUND OF THE INVENTION

The packaging of food articles such as fresh red meat, processed meatproducts, and poultry requires tough, puncture resistant, yet flexiblefilm materials. The films must be substantially impermeable to oxygen,in order to prevent spoilage of the food product and to maintain vacuumwhere vacuum packaging is employed. It is also important that the filmsbe substantially impermeable to moisture, in order to prevent leakagefrom within the package.

Oriented amide polymers, hereinafter referred to as nylons, are wellknown in the packaging industry for their toughness, punctureresistance, and oxygen barrier properties. The best oxygen barrierproperties of oriented nylon films generally occur when the nyloncontains zero or low amounts of absorbed moisture. As the moisturecontent increases, the oxygen barrier properties of most oriented nylonsdeteriorate. When the application involves exposure of the film to highhumidity or other moist conditions, it becomes desirable to encapsulatethe nylon between layers having relatively low permeability to moisture,in order to keep the nylon dry. It is also desirable that one of thelayers have good heat seal properties. Resins which have both good heatsealability and are substantially impermeable to moisture includevarious polyethylenes, ethylene copolymers and ionomers. Oriented nylonfilms are currently used alone and in combination with these heatsealable and moisture resistant layers.

In the packaging of red meat, for instance, an inner layer ofpolyethylene, ethylene vinyl acetate, or ionomer acts as a sealant layerand prevents permeation of moisture from within the package. A barrierlayer of nylon, such as Nylon 6 (polycaproamide) manufactured by AlliedCorporation, protects the meat from exposure to oxygen from theatmosphere, thus preventing spoilage. An outer layer of polyethylene orethylene vinyl acetate protects the nylon from exposure to moisture fromthe atmosphere.

In a typical process for producing multilayer films containing orientednylon, the nylon film is oriented by heating to a softened state belowthe melting point and stretching the softened material. Manyconventional nylon resins crystallize very rapidly and have meltingpoints well in excess of the adjacent polyethylene layers. Because thenylon and polyethylene tend to have different stretchingcharacteristics, the nylon must generally be oriented separately and inadvance of its combination with the adjacent polyethylene layers. Thecombination of the oriented nylon with the adjacent layers is thenaccomplished using a conventional lamination process. This requires aspecial adhesive, typically a polyurethane type adhesive applied with acoater-laminator.

Another problem with current multilayer oriented nylon structures isthat, while the polyethylene generally protects the nylon from moisture,some moisture gradually seeps in from either the packaged food articleor the atmosphere and is absorbed by the nylon. This causes an increasein oxygen permeability which shortens the shelf life of sensitive foods.

Because of recent growth in the market for barrier films there currentlyexists an industrywide search for films with improved barrier propertiessuch as low oxygen permeability and low water permeability. For economicreasons, there is also a demand for an oriented nylon multilayer filmwhich can be produced by a coextrusion process. Production of multilayerfilms by coextrusion is more economical than lamination methods of theprior art.

It is therefore an object of the present invention to provide amultilayer film structure having low oxygen permeability and preferablylow water permeability.

It is a further object of the present invention to provide a multilayerfilm structure comprising a nylon barrier layer having a low oxygenpermeability which does not increase as the nylon gradually absorbsmoisture.

A still further object of the invention is to provide a multilayer filmstructure comprising a nylon barrier layer which can be producedeconomically by a coextrusion process.

A still yet further object of the present invention is to provide amultilayer film structure comprising a nylon containing barrier layerwhich may be oriented in combination with polymer materials that havemelting points below the glass transition temperature of the nylon.

It is to be understood that additional objectives which will becomeapparent in view of the specification are also contemplated. Further,these objectives are not to be considered a limitation of the presentinvention, the spirit and scope of which is delineated in the appendedclaims.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, there isprovided an oriented multi-layer structure having a barrier layer, afirst layer on one side of the barrier layer, and a second layer on theother side of the barrier layer. The first and second layers havemelting points of at least about 115° C. The barrier layer comprisesamorphous nylon having a glass transition temperature greater than thehigher of the two melting points, or higher than the melting point ofthe first and the second layer. The film may be single axis or biaxiallyoriented. In accordance with a preferred embodiment of the invention,the amorphous nylon of the barrier layer comprises Selar (trademark)Polyamide 3426 Barrier Resin, an amorphous nylon (polyamide) resinmanufactured by and available from the Du Pont Company.

In accordance with another embodiment of the present invention there isprovided a process for producing an oriented multilayer film. Theprocess comprises the step of coextruding a barrier layer, a first layeron one side of the barrier layer, and a second layer on the other sideof the barrier layer. The first and second layers have melting points ofat least about 115° C. The barrier layer comprises amorphous nylon(polyamide) resin having a glass transition temperature greater than thehigher of the two melting points or higher than the melting point ofboth the first and second layers. After coextrusion the multi-layer filmis oriented by stretching. In accordance with still a furtherembodiment, the puncture resistance of the multilayer film may beimproved by cross-linking the multilayer structure, preferably byirradiation.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In accordance with the present invention, the barrier layer comprisesamorphous nylon (polyamide) resin having a glass transition temperaturegreater than the higher of the two melting points or higher than themelting point of the resins of both a first layer on one side of thebarrier layer and a second layer on the other side of the barrier layer.Surprisingly, it has been found that in accordance with one embodimentof the present invention the foregoing multilayer film structure can becoextruded and then oriented at temperatures below the melting points ofthe first and second layers even though the glass transition temperatureof the amorphous nylon is greater than the higher of the two meltingpoints or greater than the melting point of the adjacent layers.

The barrier layer may be formed entirely of amorphous nylon resin orother materials may be included in small portions as blends therewith aslong as the oxygen barrier property is not eliminated and the resultingblend may adequately bond to adjacent layers. Suitable blendingmaterials include hydrolyzed ethylene-vinyl acetate copolymer (EVOH),ethylene vinyl acetate (EVA) and ionomers.

In a preferred embodiment of the present invention, the amorphous nylon(polyamide) resin comprises Selar (trademark) Polyamide 3426, having aglass transition temperature of 127° C. It has been found that when thebarrier layer of a multilayer film structure comprises this particularamorphous nylon, the film structure may be oriented in combination withfirst and second layers comprising certain polyethylene resins attemperatures substantially below those expected by those skilled in theart, provided that the polyethylene has a melting point of at leastabout 115° C. Thus, any coextrusion process, followed by in-lineorientation of the multilayer structure by conventional techniques maynow be employed.

Selar Polyamide 3426, manufactured by the Du Pont Company, is believedto be substantially amorphous and has a density of 1.19 grams per cubiccentimeter. Further, according to the manufacturer's publisheddescription, Selar Polyamide 3426 has excellent melt strength (i.e.strength of the material at the extrudate temperature) and can be usedunder a much broader range of processing conditions than conventionalsemi-crystalline nylons. Selar Polyamide 3426 is otherwise characterizedas a Nylon 6I/6T resin (CAS Reg. No. 25750-23-6), manufactured by thecondensation of hexamethylenediamine, terephthalic acid, and isophthalicacid such that 65 to 80 percent of the polymer units are derived fromhexamethylene isophthalamide. (See 52 Fed. Reg. 26,667, 1987, thedisclosures of which are incorporated herein by reference). Thisparticular amorphous polyamide resin is further described andcharacterized in Bulletin E-73974 (12/85) available from Du PontCompany, said Bulletin being incorporated herein by reference.

Selar Polyamide 3426 may be formed as a barrier layer with adjacentpolyethylene layers as contemplated herein into a multilayer film byknown coextrusion techniques. As a result, sufficient inter-layeradhesion can be obtained between the Selar Polyamide and adjacent layersfor certain end uses, as for example, for selected meat packagingapplications.

Unlike the known nylon resins of the prior art, the oxygen barrierproperties of Selar Polyamide 3426 improve, rather than deteriorate, asthe film absorbs moisture. Accordingly, oriented multilayer filmscomprising Selar Polyamide 3426 in the barrier layer provide longershelf life for oxygen sensitive foods than the known nylon multilayerstructure of the prior art.

Multilayer films utilizing Selar Polyamide 3426 in the barrier layerthat are biaxially oriented are also believed to yield still furtherimprovement in oxygen barrier properties.

According to the present invention, the film structures contemplatedcomprise a plurality of layers. Preferably, the multilayer filmcomprises three layers; a barrier layer, a first outer layer on one sideof the barrier layer, and a second outer layer on the opposite side ofthe barrier layer. In general, the first and second outer layerscomprise materials having a melting point of at least about 115° C. Itis to be understood, however, that the melting points of the first andsecond layers do not have to be the same. Thus, for example, the meltingpoint of the first layer may be greater than, less than, or equal tothat of the second layer, and vice-versa. In addition, the first andsecond layers should have good heat seal and optical properties.Furthermore, though not necessary to the invention, these layers mayalso possess low water permeability to prevent spoilage. The barrierlayer, which is also referred to as the core layer, possesses low oxygenpermeability characteristics, further preventing spoilage of thepackaged product.

Though the presently preferred embodiments contemplate three layers inthe multilayer film structure, it is to be understood that additionallayers may also be present to satisfy special requirements. For example,one or more adhesive layers formed of chemically modified polyethylene,e.g. Plexar or ethylene acrylic acids, may be employed between thebarrier layer and the first or second layers. As another variation, afourth layer with special properties may be added to the layer which isintended the inside layer relative to an enclosed food product. Forexample, to achieve improved meat adhesion the practitioner may use afourth layer comprising the metal salt of an ethylene-organic acidcopolymer sold by the Du Pont Company under the product designationSurlyn 1650.

According to a preferred embodiment, in terms of film thickness whenused to form heat sealed bags, the multilayer film structure comprisesbetween about 45% to 55% and preferably about 50% of the layer on theside of the barrier layer closest to the packaged product, about 20% to30% and preferably about 25% barrier layer, and about 20% to 35% andpreferably about 25% of the layer on the side of the barrier layeropposite from the packaged product. The barrier layer is preferably inthis range to insure low water and oxygen permeability (at the low end)and avoid stretch orientation difficulties (at the high end). The layerclosest to the packaged product must be sufficiently thick to insureheat sealing integrity, and the layer on the side of the barrier layeropposite from the packaged product must be sufficiently thick towithstand physical abuse. However, it is to be understood that thethickness of individual layers and the ratios of layer thickness isbased on particular requirements of use, will be decided by thoseskilled in the art.

According to one preferred embodiment of the present invention, eitherone or both of the first and second layers comprise linear low densitypolyethylene (LLDPE). LLDPE is commonly known to those skilled in theart to have a melting point of approximately 120° C. and a densitybetween about 0.91 and 0.93 g/cm³. LLDPE has excellent heat sealproperties and a low moisture vapor transmission rate. Also, LLDPE isvery strong, making it suitable for use in multilayer films for a widevariety of barrier packaging applications.

In another embodiment of the present invention, either one or both ofthe first and second layers comprise very low density polyethylene(VLDPE). VLDPE is known to those skilled in the art to have a meltingpoint of about 120° C. and a density between about 0.88 and 0.91 g/cm³.VLDPE is especially advantageous in applications requiring improved hottack.

In accordance with the present invention, blends of any suitablethermoplastic packaging material, and preferably the foregoingpolyethylene resins may also be utilized in at least one of the firstand second layers of the multilayer barrier film. Accordingly, however,any such blend must contain at least about 90 weight percent of acomponent having a melting point greater than 115° C. Preferably, thepresent invention contemplates blends wherein at least one of the firstand second layers comprises LLDPE or VLDPE in amounts of at least 90weight percent.

Though blends comprising any suitable thermoplastic packaging materialare contemplated, blends comprising minor amounts of ethylene vinylacetate (EVA) copolymers or low density polyethylene (LDPE) arepreferably contemplated. EVA copolymer and LDPE, are known to havemelting points of about 95° C. and 110° C. respectively. Accordingly,the present invention contemplates blends comprising minor amounts ofeither EVA copolymers or LDPE in any combination with either LLDPE orVLDPE in any combination. Preferably EVA copolymer and LDPE are presentin blend amounts of up to about 10 weight percent. The particular blendsmentioned herein, however, are not to be considered a limitation of theinvention.

The EVA copolymers contemplated as minor constituent blends may bemanufactured by either the tubular or stirred methods commonly known tothose skilled in the art. Preferably, the EVA copolymers will comprisebetween about 1 to 20 percent vinyl acetate by weight and mostpreferably about 3 to 12 percent by weight. EVA copolymer is known toproduce a high clarity film having good heat seal properties.

As a further variation, certain adhesives may also be blended in thelayers, as for example an ethylene based polymer containing vinylacetate and anhydride functionally sold by the Du Pont Company under theproduct description Bynel CXA 3048.

After formation, the multilayer film of this invention is oriented bystretching in at least one direction, i.e. uniaxially in either thelongitudinal or transverse direction, or in both directions, i.e.biaxially by techniques known to those skilled in the art.

In accordance with a presently preferred embodiment of the invention,the multilayer film is manufactured by combining the amorphous nyloncontaining barrier layer with the first and second layers by coextrusionprocesses known in the art. The multilayer film is then oriented,preferably by stretching the structure in both the transverse andmachine directions in order to achieve biaxial orientation. Biaxialorientation is believed to yield still further improvement in oxygenbarrier properties.

In a highly preferred embodiment of the invention, the layers are firstcoextruded and then bi-axially oriented using a double bubble process ofthe type described in U.S. Pat. No. 3,456,044 which is incorporatedherein by reference. In this process the primary tube is simultaneouslystretched in the transverse direction by air pressure and in thelongitudinal or machine direction by the use of pinch rolls at differentspeeds. It was surprising that double bubble-extruded film demonstratedacceptable adhesion characteristics since blown films of the samecomposition showed poor adhesion characteristics.

Processing conditions contemplated by the present invention will varydepending on the type of manufacturing process used. Coextrusiontemperatures, for example, may range between approximately 175° C. and250° C. In the preferred double bubble coextrusion process, the biaxialorientation temperature must be below the melting temperature of theouter layers, and preferably between about 10° C. to 20° C. below thelower of the melting points of the outside layers.

In accordance with a particularly preferred embodiment, the amorphousnylon containing barrier layer comprises Selar Polyamide 3426 and thefirst and second layers comprise LLDPE. When manufactured, theparticular multilayer structure is coextruded using die temperatures ofabout 220°-240° C. and is biaxially oriented at an orientationtemperature of about 100° C. to 110° C. It was surprising that amultilayer film comprising SELAR and LLDPE could be bioriented.According to commercial literature available from Du Pont, Selar has aglass transition point of 127° C. Thus, one skilled in the art wouldexpect that orientation of the film would have to occur at temperaturesabove the melting point of LLDPE. It is known to those skilled in theart that LLDPE has a melting point of about 120° C.--substantially lowerthan the glass transition point of SELAR. Since according to commonlyknown orientation techniques, one usually orients at temperatures belowthe melting temperatures of one of the layer components, it would beunexpected to one skilled in the art to combine layers having meltingpoints lower than the glass transition point of SELAR since these layerswould melt at the higher orientation temperatures theoretically requiredfor SELAR.

Yet, according to the present invention, it has been found that amultilayer film having an amorphous nylon containing barrier layer, suchas SELAR, in combination with first and second layers as describedherein surprisingly can be oriented. Without being limited to theory,according to conventional processing techniques, it is known that theorientation bubble is formed after passing the coextruded film throughconventional infrared heaters. The latter are conventionally set toprovide an exit orientation temperature as measured at the outside ofthe film of about 10° C. to 20° C. below the lower of the melting pointsof the first and second layers. It is theorized that the outer layersabsorb infrared heat at one particular wave length while the amorphousnylon resin absorbs the infrared heat at various wave lengths. Thus, itis possible that infrared heat at various wave lengths may penetrate theouter portions of the co-extruded film without heating and cause theamporphous nylon to reach a temperature suitable for orientation. Theamorphous nylon appears to be receptive to heating by such penetratinginfrared waves.

Orientation is a major factor in determining the minimum melting pointof the first and second layers of the multilayer film of the presentinvention. If the orientation temperature is too low, the film structureof the present invention will not orient. Thus, even though the meltingpoints of the first and second layers are less than the glass transitiontemperature of the amorphous nylon contained in the barrier layer, themelting points must be above at least about 115° C. A minimum meltingpoint of about 115° C. will allow the orientation temperature to besufficiently high to orient the multilayer film of the presentinvention.

Many applications require multilayer barrier films with high punctureresistance. In still another embodiment of the present invention, thepuncture resistance of the multilayer film structure may be improved bycross-linking one or more layers. This may be accomplished by theinclusion of a cross-linking agent, but is preferably done by treatmentwith a dosage of irradiation subsequent to orientation (i.e.post-irradiation). Alternatively a single layer may be extruded,oriented and then irradiated, followed by coating lamination of theother layers. Various irradiation procedures are described in U.S. Pat.No. 4,044,187. Preferably the dosage contemplated is small and betweenabout 1 Mrad and about 10 Mrad. Most preferably, the irradiation dosageis about 2-4 Mrad.

The multilayer film of this invention is preferably produced by thecoextrusion-double bubble method. The multilayer film may also befabricated by extrusion coating, wherein a base tube is extruded andsucceeding layers are surface coated on the base tube in a manner suchas that disclosed in U.S. Pat. No. 3,741,253. Also, the multilayer filmmay be slot cast and biaxially stretched by tentering before theresulting sheet is fabricated into bags. Still further, the inventivemultilayer film may be fabricated by producing separate film layers andthen laminating the layers together.

This multilayer film is wound up as flattened, seamless, tubular film tobe used later to make bags. This may be accomplished by end seals,typically made by transverse heat isolating across the width offlattened tubing followed by severing the tubing so that the transverseseal forms the bag bottom. Alternatively, side-seal bags may be formedin which the transverse seals form the bag sides and one edge of thetubing forms the bag bottom.

Various conventional additives such as slip agents, anti-block agents,plasticizers and pigments can be incorporated in the multilayer film ofthis invention, as is well-known in the art.

The following examples are intended as illustrations of the presentinvention and are not to be considered as limiting. It is to beunderstood that equivalents of the present invention are also intended,the spirit and scope of which is defined in the appended claims.

EXAMPLE 1

A three layer biaxially oriented coextruded structure was produced usinga double bubble coextrusion process. The barrier layer consisted ofSelar Polyamide 3426 Barrier Resin (glass transition 127° C.)manufactured by Du Pont. Both the first outer layer and the second outerlayer consisted of UCC 7510 LLDPE (Density 0.920 g/cc, Melt Index 0.65g/10 min., Melting Point 120° C.) manufactured by Union Carbide. Thelayer thicknesses were 20% for the barrier layer and 40% for each of theouter layers. Extrusion temperatures were 425° F. (218° C.) for thebarrier layer and 350° F. (177° C.) for both outer layers. The diediameter was 1.25 inches. The primary tubing was 3.75 inch flat widthand the secondary tubing was 10 inch flat width with a thickness of 2.65mils. The biorientation temperature was about 105° C.

The resulting multilayer film had a machine direction tensile strengthof 7,500 psi and a transverse direction tensile strength of 10,000 psi.The multi-layer film had an oxygen transmission rate of 2.6 cc/100 in²/24 hrs. The adhesion between layers was satisfactory for use of thefilm in the form of a bag for packaging of fresh red meat. This wasdemonstrated by a tensile strength test based on ASTM Method D882. Theoriented structure provided a smooth stress-strain curve with noevidence of layer separation up to the break point.

A similar structure (nonoriented) was produced by a conventional blownfilm coextrusion process at similar processing conditions. The layerthicknesses were again 20% for the barrier layer and 40% for each outerlayer. The resulting film had a thickness of 4.5 mils and a flat widthof 6.5 inches. The blown film structure delaminated readily and couldnot be used as a composite. This illustrates that the double bubbleprocess provides improved interlayer adhesion.

EXAMPLE 2

A three layer biaxially oriented coextruded structure was produced by adouble bubble coextrusion process at extrusion conditions similar tothose in Example 1. The barrier layer consisted of Selar Polyamide 3426Barrier Resin. Both the first outer layer and the second outer layerconsisted of UCC 7510 LLDPE. Some of the film was treated with anirradiation dosage of 3 Mrad. The untreated film had an impact strengthof 0.3 kg-c,/mil. The irradiated film had an impact strength of 1.0kg-cm/mil. This comparison demonstrates the improved puncture resistanceattainable by cross-linking the multilayer film of this invention.

What is claimed is:
 1. An oriented multilayer film comprising a barrierlayer, a first layer on one side of said barrier layer and a secondlayer on the opposite side of said barrier layer, wherein said firstlayer and said second layer have melting points of at least about 115°C. and said barrier layer comprises amorphous nylon having a glasstransition temperature greater than the higher of the melting point ofsaid first layer and said second layer.
 2. The oriented multilayer filmof claim 1 wherein said barrier layer comprises nylon 6I/6T.
 3. Theoriented multilayer film of claim 1 wherein at least one of said firstlayer and said second layer comprises linear low density polyethylene.4. The oriented multilayer film of claim 1 wherein both of said firstand said second layers comprise linear low density polyethylene.
 5. Theoriented multilayer film of claim 1 wherein at least one of said firstlayer and said second layer comprises very low density polyethylene. 6.The oriented multilayer film of claim 1 wherein both of said first andsaid second layers comprise very low density polyethylene.
 7. Theoriented multilayer film of claim 1 wherein at least one of said firstand second layers comprises linear low density polyethylene in an amountof at least 90 weight percent and ethylene vinyl acetate in an amount upto about 10 weight percent.
 8. The oriented multilayer film of claim 1wherein at least one of said first and second layers comprises very lowdensity polyethylene in an amount of at least 90 weight percent andethylene vinyl acetate in an amount up to about 10 weight percent. 9.The oriented multilayer film of claim 1 wherein at least one layer ofsaid multilayer film is cross-linked.
 10. The oriented multilayer filmof claim 1 wherein the entire multilayer film is cross-linked with anirradiation dosage of approximately 1-10 Mrad.
 11. The oriented film ofclaim 1 wherein said film is a tubular film.
 12. The oriented film ofclaim 1 wherein at least one of said first layer and said second layeris an outermost layer of said multilayer film.
 13. The oriented film ofclaim 1 wherein at least one of said first layer and said second layeris directly adhered to said barrier layer.
 14. The oriented film ofclaim 1 wherein both of said first and second outer layers are directlyadhered to opposite sides of said barrier layer.
 15. The oriented filmof claim 1 wherein said barrier layer consists essentially amorphousnylon.
 16. The oriented film of claim 1 wherein said barrier layer hasthickness of about 20% to about 30% of the total film thickness.
 17. Anoriented multilayer film comprising a barrier layer, a first layer onone side of said barrier layer and a second layer on the opposite sideof said barrier layer, wherein said first layer and said second layerhave melting points of at least about 115° C. and said barrier layercomprises nylon 6I/6T polymer having from 65 to 80 percent of itspolymer units derived from hexamethylene isophthalamide.
 18. Theoriented multilayer film of claim 17 wherein at least one of said firstlayer and said second layer comprises linear low density polyethylene.19. The oriented multilayer film of claim 17 wherein both of said firstand said second layers comprises linear low density polyethylene. 20.The oriented multilayer film of claim 17 wherein at least one of saidfirst layer and said second layer comprises very low densitypolyethylene.
 21. The oriented multilayer film of claim 17 wherein bothof said first and said second layers comprises very low densitypolyethylene.
 22. The oriented multilayer film of claim 17 wherein atleast one of said first and second layers comprises linear low densitypolyethylene or very low density polyethylene in an amount of at least90 weight percent and ethylene vinyl acetate in an amount up to about 10weight percent.
 23. The oriented multilayer film of claim 17 whereinsaid barrier layer consists essentially of said nylon 6I/6T.
 24. Theoriented multilayer film of claim 17 wherein at least one layer of saidmultilayer film is cross-linked.
 25. The oriented multilayer film ofclaim 17 wherein the entire multilayer film is cross-linked with anirradiation dosage of approximately 1-10 Mrad.
 26. A coextrudedbiaxially oriented multilayer film comprising a barrier layer, a firstlayer on one side of said barrier layer and a second layer on theopposite side of said barrier layer, wherein said first layer and saidsecond layer have melting points of at least about 115° C. and saidbarrier layer comprises amorphous nylon.
 27. The biaxially oriented filmof claim 26 wherein at least one of said first layer and said secondlayer comprises linear low density polyethylene.
 28. The biaxiallyoriented multilayer film of claim 26 wherein both of said first and saidsecond layers comprise linear low density polyethylene.
 29. Thebiaxially oriented film of claim 26 wherein at least one of said firstlayer and said second layer comprises very low density polyethylene. 30.The biaxially oriented film of claim 26 wherein both of said first andsaid second layers comprise very low density polyethylene.
 31. Theoriented multilayer film of claim 26 wherein at least one of said firstand second layers comprises linear low density polyethylene or very lowdensity polyethylene in an amount of at least 90 weight percent andethylene vinyl acetate in an amount up to about 10 weight percent. 32.The oriented multilayer film of claim 26 wherein said amorphous nyloncomprise nylon 6I/6T.
 33. The biaxially oriented film of claim 26wherein at least one layer of said multilayer film is cross-linked. 34.The biaxially oriented film of claim 26 wherein the entire multilayerfilm is cross-linked with an irradiation dosage of approximately 1-10Mrad.
 35. A process for producing an oriented multilayer film comprisingthe steps of:(a) coextruding a barrier layer, a first layer on one sideof said barrier layer and a second layer on the opposite side of saidbarrier layer, wherein said first layer and said second layer havemelting points of at least about 115° C. and said barrier layercomprises amorphous nylon having a glass transition temperature greaterthan the higher of the melting point of said first layer and said secondlayer; and (b) heating with infrared heaters and stretching saidmultilayer film under conditions sufficient to produce an orientedmultilayer film wherein said heating conditions are set to provide anexit orientation temperature, as measured at the outside of the film,below both the melting points of said first and second layers and belowthe glass transition temperature of the barrier layer.
 36. The processof claim 35 wherein said multi-layer film is produced by a double bubblecoextrusion process.
 37. The process of claim 35 wherein saidmulti-layer film is cross-linked.
 38. The process of claim 35 whereinsaid multi-layer film is cross-linked by exposure to an irradiationdosage of approximately 1-10 Mrad.
 39. The process of claim 35 whereinsaid barrier layer comprises nylon 6I/6T.
 40. The process of claim 35wherein said at least one of said first and second layers comprises apolymer resin selected from the group consisting of linear low densitypolyethylene, very low density polyethylene, and combinations thereof.41. The process of claim 35 wherein said multi-layer film is biaxiallystretched.
 42. The process of claim 35 wherein said exit orientationtemperature is about 105° C.